Personal Rapid Transit (Hereinafter referred to as PRT) is a public transportation system which provides passengers a non-stop trip from origin to destination in a small personal vehicle. The vehicles are fully automated and run on a small light weight aerial guideway which can be located above streets, through buildings etc. The PRT system provides a high transportation capacity by operating the vehicles at very short headways of about 0.5 seconds. This provides a practical capacity of about 6000 vehicles per hour on a single guideway.
In order to operate safely at these headways, each vehicle is equipped with a sophisticated computer control system which varies the thrust of the linear induction motors to provide acceleration and braking. Under normal operating conditions braking of moving vehicles will be accomplished by reversing the thrust direction of the linear motors.
However, when the vehicle stops at a station to unload and load passengers and when the vehicle is parked in storage, the separate parking brake must be applied. When there is any malfunction in a vehicle or failure of the power supply of a moving vehicle which may lead to a dangerous situation, it will be necessary to apply the emergency brake.
Conventional braking system mechanisms for wheeled vehicles are well known, but are not applicable for PRT. These systems consist of a body mounted mechanism which applies a frictional device to the rotating parts of the wheel assembly. Deceleration is accomplished by reducing the speed of rotation of the wheel which thus transmits the braking force to the running surface.
Some vehicles achieve braking by applying a brake shoe to the guideway surface or track. These vehicles rely on an electromagnetic force to apply the brake shoe to the track rail, but the operation of the brake shoe necessarily requires an external electric power source.
Other types of guideway brakes apply a mechanically operated brake shoe to the rail or running surface, and the braking force in this case depends upon the weight of the vehicle and the coefficient of friction between the brake shoe and the running surface. This coefficient is generally in the range of 0.3 to 0.7 in dry weather conditions, but it can be reduced to a small fraction of that coefficient under adverse weather conditions such as snow, ice or rain.
The PRT vehicles are propelled by the thrust generated by a linear induction motor which acts against a reaction rail mounted on the guideway. Normally, there is no mechanical contact between the linear induction motor and the reaction rail. The PRT vehicles wheels simply provide support and guidance to the vehicles. The wheels are not required to transmit propulsion torque nor provide adequate braking because they are smooth tired and run on a smooth stainless steel guideway lubricated to reduce rolling resistance.
This means that a conventional braking system can not be used in this PRT system, thus a separate braking system which can serve as a parking brake as well as an emergency brake is required. This brake must be able to operate in the absence of electric power.